Heat in the roof cavity and coolness under the floor

Roof cavities are hot. Just ask anyone who has to work up there. Even in winter they are very warm. In this area most houses have “whirly gigs” to pump this heat out.

Earlier in the year I wrote about how even in winter a light brick will heat up more than 8° above the ambient temperature, and a dark brick will heat up to nearly 20° warmer. So taking that idea and applying it to the roof, you can easily see why a roof is so hot.

We didn’t do the tests in summer, but anyone who ever ventured into the roof cavity in the middle of summer knows that it is a furnace. Hence the whirly gigs.

But in winter that heat is an asset. There is all this talk about using solar power, but the fact is there is a huge amount of solar energy being captured above our heads every day. And in winter it is sucked out by the whirly gigs and replaced by cold air.

At the same time, under the house has the opposite types of problems. In winter it becomes too cold and damp. Dampness becomes an issue. Every house inspection I have had says “needs more ventilation”. But in summer it is so nice and cool under there.

So I came up with a simple solution. I have a vent that goes from the roof to under the house. Finding a location for it was a bit of an issue. I had to sacrifice either some cupboard space or space in the entrance foyer. The entrance foyer lost out and now has pine boards hiding the ducting. I may get around to making it look better one day.

But under the house I have a fan. Ideally it should have been up in the roof (apparently it is more efficient that way) but I had easy access to a power point under the house.

And here the ground breaking part of it all…

… in summer I take the cool air from under the house and pump it into the roof cavity. This cools the roof space down considerably and helps to push the hot air out. And

… in winter I take the warm air from the roof and pump it under the house. This warms up under the house a bit, helping keep it drier, and possibly help heat the house.

Practically I don’t know how much of an impact it is having on my heating and cooling bills. The fan itself is low power so is cheap to run, and the impact it has in summer is huge. So it should have a flow on effect on the power bill.

The system can have many improvements made. At the moment it is manual. I would love to automate it with an external temperature sensor. Then it would really start to fly. A couple of temperature loggers scattered around the place would then let me know if it is really working. The benefits of selling temperature loggers.

So if there are any experts out there, is this a good DIY solution?

But tomorrow I will talk about a commercial system that trumps my idea.